In vivo cardiac role of migfilin during experimental pressure overload.

AIMS: Increased myocardial wall strain triggers the cardiac hypertrophic response by increasing cardiomyocyte size, reprogramming gene expression, and enhancing contractile protein synthesis. The LIM protein, migfilin, is a cytoskeleton-associated protein that was found to translocate in vitro into the nucleus in a Ca(2+)-dependent manner, where it co-activates the pivotal cardiac transcription factor Csx/Nkx2.5. However, the in vivo role of migfilin in cardiac function and stress response is unclear. METHODS AND RESULTS: To define the role of migfilin in cardiac hypertrophy, we induced hypertension by transverse aortic constriction (TAC) and compared cardiac morphology and function of migfilin knockout (KO) with wild-type (WT) hearts. Heart size and myocardial contractility were comparable in untreated migfilin KO and WT hearts, but migfilin-null hearts presented a reduced extent of hypertrophic remodelling in response to chronic hypertensile stress. Migfilin KO mice maintained their cardiac function for a longer time period compared with WT mice, which presented extensive fibrosis and death due to heart failure. Migfilin translocated into the nucleus of TAC-treated cardiomyocytes, and migfilin KO hearts showed reduced Akt activation during the early response to pressure overload. CONCLUSIONS: Our findings indicate an important role of migfilin in the regulation of cardiac hypertrophy upon experimental TAC.

Cre recombinase induces DNA damage and tetraploidy in the absence of loxP sites.

The spatiotemporal manipulations of gene expression by the Cre recombinase (Cre) of bacteriophage P1 has become an essential asset to understanding mammalian genetics. Accumulating evidence suggests that Cre activity can, in addition to excising targeted loxP sites, induce cytotoxic effects, including abnormal cell cycle progression, genomic instability, and apoptosis, which can accelerate cancer progression. It is speculated that these defects are caused by Cre-induced DNA damage at off-target sites. Here we report the formation of tetraploid keratinocytes in the epidermis of keratin 5 and/or keratin 14 promoter-driven Cre (KRT5- and KRT14-Cre) expressing mouse skin. Biochemical analyses and flow cytometry demonstrated that Cre expression also induces DNA damage, genomic instability, and tetraploidy in HCT116 cells, and live-cell imaging revealed an extension of the G 2 cell cycle phase followed by defective or skipping of mitosis as cause for the tetraploidy. Since tetraploidy eventually leads to aneuploidy, a hallmark of cancer, our findings highlight the importance of distinguishing non-specific cytopathic effects from specific Cre/loxP-driven genetic manipulations when using Cre-mediated gene deletions.

Mutations in the paxillin-binding site of integrin-linked kinase (ILK) destabilize the pseudokinase domain and cause embryonic lethality in mice.

Integrin-linked kinase (ILK) localizes to focal adhesions (FAs) where it regulates cell spreading, migration, and growth factor receptor signaling. Previous reports showed that overexpressed ILK in which Val(386) and Thr(387) were substituted with glycine residues (ILK-VT/GG) could neither interact with paxillin nor localize to FA in cells expressing endogenous wild-type ILK, implying that paxillin binding to ILK is required for its localization to FAs. Here, we show that introducing this mutation into the germ line of mice (ILK-VT/GG) caused vasculogenesis defects, resulting in a general developmental delay and death at around embryonic day 12.5. Fibroblasts isolated from ILK-VT/GG mice contained mutant ILK in FAs, showed normal adhesion to and spreading on extracellular matrix substrates but displayed impaired migration. Biochemical analysis revealed that VT/GG substitutions decreased ILK protein stability leading to decreased ILK levels and reduced binding to paxillin and α-parvin. Because paxillin depletion did not affect ILK localization to FAs, the embryonic lethality and the in vitro migration defects are likely due to the reduced levels of ILK-VT/GG and diminished binding to parvins.

FGF receptors 1 and 2 are key regulators of keratinocyte migration in vitro and in wounded skin.

Efficient wound repair is essential for the maintenance of the integrity of the skin. The repair process is controlled by a variety of growth factors and cytokines, and their abnormal expression or activity can cause healing disorders. Here, we show that wound repair is severely delayed in mice lacking fibroblast growth factor receptors (FGFR) 1 and 2 in keratinocytes. As the underlying mechanism, we identified impaired wound contraction and a delay in re-epithelialization that resulted from impaired keratinocyte migration at the wound edge. Scratch wounding and transwell assays demonstrated that FGFR1/2-deficient keratinocytes had a reduced migration velocity and impaired directional persistence owing to inefficient formation and turnover of focal adhesions. Underlying this defect, we identified a significant reduction in the expression of major focal adhesion components in the absence of FGFR signaling, resulting in a general migratory deficiency. These results identify FGFs as key regulators of keratinocyte migration in wounded skin.

Loss of migfilin expression has no overt consequences on murine development and homeostasis.

Migfilin is a LIM-domain-containing protein of the zyxin family of adaptor proteins and is found at cell-matrix and cell-cell adhesion sites and in the nucleus. In vitro studies have suggested that migfilin promotes ß1 integrin activity, regulates cell spreading and migration and induces cardiomyocyte differentiation. To test directly the function of migfilin in vivo, we generated a migfilin-null mouse strain. Here, we report that loss of migfilin expression permits normal development and normal postnatal aging. Fibroblasts and keratinocytes from migfilin-null mice display normal spreading and adhesion, and normal integrin expression and activation. The migration velocity and directionality of migfilin-null embryonic fibroblasts were normal, whereas the velocity of migfilin-null keratinocytes in wound scratch assays was slightly but significantly reduced. Our findings indicate that the roles of migfilin are functionally redundant during mouse development and tissue homeostasis.